Electrically controllable chirality in a nanophotonic interface with a 2D semiconductor

Waveguided optical modes in nanophotonic structures display circularly polarized evanescent fields with wavevector-dependent, transverse spin angular momentum. This optical spin-orbit coupling allows propagation direction-dependent interactions with circularly dichroic materials, yielding chiral light-matter interfaces. Electrical tuning of interface chirality would aid active, switchable non-reciprocity in on-chip optoelectronic and photonic circuitry, but remains an outstanding challenge. Here, we report electrically controllable chirality in a nanophotonic interface with atomically thin monolayer tungsten diselenide (WSe2). We fabricate titanium dioxide (TiO2) waveguides directly on the surface of low disorder, boron nitride-encapsulated WSe2. Following integration, we show that emission from excitonic states into the waveguide can be electrically switched between balanced and directionally biased. Furthermore, we demonstrate that our nanophotonic waveguide can function as a near-field source for valley(spin)-polarized exciton fluxes. Our versatile fabrication approach enables deterministic integration of photonics with low disorder van der Waals heterostructures and opens new pathways towards optically driving their excitonic and charge carrier behavior.